Background
In the new energy high-voltage direct-current transmission project, a direct-current energy consumption device is a vital device. The direct current energy consumption device is mainly applied to the application scene that new energy is transmitted through direct current, if a transmitting end is new energy such as a wind power plant, when a receiving end alternating current system breaks down, energy is accumulated on a direct current side due to the fact that power is transmitted by the receiving end firstly, and direct current voltage is increased, and safe operation of equipment is damaged. The purpose of the energy consumption device when the energy consumption device is installed in the receiving end converter station is to ensure that the energy consumption device can be put into the receiving end converter station when the receiving end converter station has an alternating current fault, and the system can be ensured to operate stably.
The technical solution disclosed in the document (CN 108258723A) is to put an energy consuming device on the ac side, so as to solve the problem that when the dc transmission line fails, a braking resistor is put on the ac side to consume surplus power. This solution is feasible in land based wind farms. When the scheme is applied to an offshore platform, the alternating current energy consumption device is installed at the sea of a sending end, so that the larger economic cost is increased, and the alternating current energy consumption device is not suitable for an offshore flexible direct current transmission system.
The technical solution disclosed in the document (CN 107994613B) is that the energy consuming device determines whether to put in or withdraw by detecting the dc side voltage, and puts in when the dc side voltage is higher than 1.15pu, and withdraws when the dc side voltage is lower than 0.9 pu. In actual engineering, the valve side fault can be irradiated to be that the direct current side voltage is higher than 1.15pu and even higher, and at the moment, if an energy consumption device is put into use, the energy consumption device can be caused to work at a larger current, so that the energy consumption device adopts a higher-grade device, and the equipment investment is increased. Therefore, the fault type cannot be accurately judged only by the direct-current voltage judgment, and the misoperation of the device can be caused.
The technical solution disclosed in the document (CN 107994613B) is to determine the fault type by detecting ac/dc voltage, but the determination of the fault type is not used for controlling the energy consuming module, but is used for switching the control mode of the MMC.
From the above, none of the above documents discloses how to avoid the dc energy consuming device from being dropped or withdrawn by mistake and to deal with the problem of the relationship better than the flexible dc control protection system.
The energy consumption device can detect the voltage of the direct current bus and the current of the energy consumption branch circuit, and the conventional strategy only depends on the direct current voltage to judge the direct current energy consumption input condition, so that the energy consumption is more likely to be input by mistake, and the requirement on energy consumption equipment is further improved. Meanwhile, two information quantities of the direct-current bus voltage and the current of the energy consumption branch circuit cannot help the energy consumption branch circuit to accurately judge the fault type of the direct-current system, surplus power to be consumed cannot be accurately known, if the energy consumption branch circuit accurately judges the fault type and calculates the surplus power, information of other parts of the flexible direct-current system also needs to be acquired to complete the function, the flexible direct-current control protection system can accurately judge the fault type and the surplus power, the control protection system and the energy consumption body control system inherently have an optical fiber link channel, based on cost consideration and engineering feasibility and usability consideration of the original optical fiber channel and the like, the flexible direct-current control protection fault judgment and surplus power calculation capacity is utilized, and the energy consumption equipment body control is combined to form an economically feasible and optimal technical scheme. Meanwhile, in order to ensure that the energy consumption device can continuously operate when the communication between the energy consumption device and the control and protection system fails, the invention provides a local control method of the energy consumption device after the communication failure, and the power transmission reliability of the flexible and straight system is ensured.
Disclosure of Invention
The invention aims to provide a control system and a control method of a direct current energy consumption device, which can accurately input required energy consumption power according to different fault types and communication states of a control system, stably control direct current voltage during a fault period, and improve the stability and reliability of a power transmission system.
In order to achieve the above purpose, the solution of the invention is:
a control system of a direct current energy consumption device comprises a flexible direct current control protection system and an energy consumption device control system;
the flexible direct current control protection system is used for acquiring alternating current and direct current signals and equipment running states of the flexible direct current power transmission system and sending direct current energy consumption switching instructions and surplus power to the energy consumption device control system when the alternating current system fails and switching conditions are met;
the energy consumption device control system is connected with the energy consumption device, collects the state of the energy consumption device and sends a control command to the energy consumption body according to the requirement;
when the communication is normal, the energy consumption device control system receives a direct current energy consumption switching instruction and an surplus power value sent by the flexible direct current control protection system, and the energy consumption device control system switches matched energy consumption power in combination with the state of the energy consumption device;
when the communication is in fault, the control system of the energy consumption device determines whether to put in the energy consumption device according to the direct current voltage and current signals acquired by the control system, and puts in corresponding energy consumption power when needing to put in.
The flexible direct current control protection system and the energy consumption device control system are communicated through optical fibers.
The energy consumption device control system is connected with the energy consumption device through an optical fiber or a cable.
The control method based on the control system of the direct current energy consumption device comprises the following steps:
step 1, a flexible direct current control protection system acquires alternating current and direct current signals of a flexible direct current power transmission system and an equipment running state, and sends a direct current energy consumption switching instruction and surplus power to an energy consumption device control system when an alternating current system fails and switching conditions are met;
step 2, if the communication is normal, the energy consumption device control system inputs matched energy consumption power by combining the states of the energy consumption devices according to the direct current energy consumption input and output instruction and the surplus power value sent by the flexible direct current control protection system;
if the communication is in fault, the control system of the energy consumption device determines whether to put the energy consumption device into operation or not according to the direct current voltage and current signals acquired by the control system, and puts corresponding energy consumption power into operation when the energy consumption device needs to be put into operation.
In the step 1, the throwing-withdrawing conditions are as follows: surplus power is larger than a first energy consumption input set value, and direct-current voltage is larger than or equal to the energy consumption input set value and lasts for Tm_set1。
In the step 1, the surplus power calculation mode is as follows: prest=Psend-Pdc-PlossWherein P isrestFor surplus power, PsendIs as followsFront end transmission power, P, of DC systemdcFor actual power delivery, P, of the receiving converter station during a faultlossAre losses of the dc cable and the converter station.
In thestep 2, the control system of the direct current energy consumption device receives the surplus power PrestAfter the input instruction is added, calculating the input energy consumption input reference number as Prest/Pcm,PcmAnd obtaining the accurate input energy consumption number and inputting corresponding energy consumption through the difference between the real-time bus voltage and the control voltage during the energy consumption input period through proportional relation or PI fine adjustment reference number for the divisible minimum energy consumption power.
And the flexible direct current control protection system sends an exit instruction to the energy consumption device control system after detecting that the fault disappears, and the energy consumption device control system controls the energy consumption device to exit energy consumption after receiving the exit instruction.
In thestep 2, if the communication between the flexible direct current control protection system and the energy consumption device control system fails, when the direct current voltage is greater than or equal to the second energy consumption input set value Udcchop_set2And after a period of time Tm_set2The energy consuming device is started and put into operation according to Udcchop_set3→Udcchop_set2Corresponding to the corresponding relation of 0 → N energy consumption numbers, where N corresponds to the rated energy consumption number, Udcchop_set3The set value is withdrawn for energy consumption.
In thestep 2, if the flexible dc control protection system and the energy consumption device control system have a communication fault, when the dc voltage is less than the energy consumption exit set value and a certain time T passesm_set3And the energy consumption device is withdrawn.
After the scheme is adopted, the invention has the beneficial effects that:
(1) when the communication of the flexible direct current control protection and energy consumption body control system is normal: the characteristics that the flexible direct-current control protection system can be monitored globally are fully utilized to be combined with the control of the energy consumption device body, so that the energy consumption device is accurately switched, meanwhile, the mistaken switching of the energy consumption device is avoided, the oscillation process when a fault just occurs is avoided, and the stable state can be reached more quickly;
(2) after communication failure, a local control strategy of the energy consumption device in a self-adaptive communication state is provided, the situation that the direct current energy consumption device is forced to quit operation when communication failure occurs is avoided, and the risk of shutdown of a direct current transmission system is reduced.
Detailed Description
The technical solution and the advantages of the present invention will be described in detail with reference to the accompanying drawings.
The invention provides a control system of a direct current energy consumption device, which comprises a flexible direct current control protection system and an energy consumption device control system, wherein the flexible direct current control protection system and the energy consumption device control system are communicated through optical fibers, the flexible direct current control protection system detects information such as direct current voltage, alternating current voltage, direct current, bridge arm voltage, bridge arm current and the like of a converter station, judges the state, the fault type and the state of the system, calculates surplus power to determine energy consumption input and sends a switching command to the energy consumption system at the same time.
The flexible direct current control protection system is a control system of the whole flexible direct current power transmission and is used for collecting alternating current and direct current signals of the flexible direct current power transmission system and the running state of equipment so as to monitor the real-time state of the whole system. When the flexible-direct control protection system monitors that the alternating current system fails, and detects that the surplus power is greater than the energy consumption power input set value: prest≥Pchop_set1And simultaneously, the direct-current voltage is more than or equal to the energy consumption input set value 1: u shapedc≥Udcchop_set1And continues for a period of time Tm_set1And the flexible-direct control protection system sends an input instruction and an excess power value to the energy consumption device control system. At this time, the control system of the DC energy consumption device receives PrestAfter the input instruction is added, calculating the input energy consumption input reference number as Prest/Pcm,PcmIs divided intoAnd the cut minimum energy consumption power passes through the difference between the real-time bus voltage and the control voltage during the energy consumption input period, and the accurate input energy consumption number is obtained through the proportional relation or PI fine adjustment reference number so as to input corresponding energy consumption. And the flexible direct current control protection system sends an exit instruction to the energy consumption device after detecting that the fault disappears. And the energy consumption device receives the exit instruction and then exits the energy consumption.
The energy consumption device control system is connected with the energy consumption device through an optical fiber or a cable, collects the state of the energy consumption device and sends a control command to the energy consumption body according to the requirement to realize monitoring and control of the energy consumption device, and the energy consumption device control system measures direct-current voltage and energy consumption branch current. When the communication between the flexible direct current control protection system and the energy consumption device control system fails, when the direct current voltage is more than or equal to the energy consumption input set value 2: u shapedc≥Udcchop_set2And after a period of time Tm_set2The energy consuming device is started and put into operation according to Udcchop_set3→Udcchop_set2Corresponding to the corresponding relation of 0 → N energy consumption numbers, and N corresponding to the rated energy consumption number.
When the flexible direct current control system and the energy consumption device control system are in communication failure, when the direct current voltage is smaller than the energy consumption exit set value: u shapedc<Udcchop_set3And after a certain time Tm_set3And the energy consumption device is withdrawn.
When the converter station is detected to have an alternating current fault, the flexible direct current protection system calculates surplus power and direct current voltage, and if the surplus power is larger than a set value and the direct current voltage rises, a putting-in instruction is sent to the energy consumption device. And the simultaneous control system sends the calculated surplus power or the number of the sub-modules to the control system of the energy consumption device body.
The surplus power calculation formula is as follows:
Prest=Psend-Pdc-Ploss
in the formula, PrestFor surplus power, PsendDelivering power, P, to the current DC system's transmitterdcFor actual power delivery, P, of the receiving converter station during a faultlossIs a DC cable and a current converterThe station is lost. P may also belossAnd setting the value to be 0, and considering the loss of the direct current cable and the converter station at the energy consumption power input set value.
Normally there is always Pdc≈PsendI.e. Prest0. When the AC side of the sending end fails, PdcThe delivery capacity is limited, at which point P appearsrest≥Pchop_setCombined with a DC voltage boost (U)dc≥Udcchop_set) And energy consumption devices are required to be input, and surplus power is consumed. Pchop_set>Ploss,Udcchop_setAnd selecting the direct current voltage set value larger than the receiving terminal station.
The table below shows the upper limit of the direct current transmission power and the energy consumption switching strategy under different metallic fault types of the receiving-end near-end alternating current system.
After the fault is cleared or disappears, the control and protection system judges that the fault disappears according to the voltage of the alternating current system, and sends an exit instruction to the energy consumption device, so that the situation that certain energy consumption conditions cannot exit or the energy consumption conditions exit by mistake is avoided.
The direct current energy consumption device is a distributed energy consumption device with distributed power devices/modules and energy consumption resistors or a mixed energy consumption device with distributed power devices/modules and concentrated energy consumption resistors. The more energy consuming devices that are put into modules, the more power they consume.
The control system of the energy consumption device constantly keeps communication with the flexible direct current protection system and detects the communication state, and when the communication is normal, the control scheme is as follows:
the energy consumption device body controls and receives the input instruction and the surplus power value of the flexible direct current protection system. After the energy consumption is put into use, the energy consumption device is started, the number of the put-in sub-modules is determined according to the surplus power auxiliary direct current voltage, and therefore the direct current voltage is controlled to be at a rated voltage or a certain voltage value, and the stable operation of the system is guaranteed.
The energy consumption device body controls and receives an energy consumption exit instruction of the flexible direct current protection system, the energy consumption device reduces the number of the input sub-modules according to a preset speed until the number of the input sub-modules is 0, and the whole energy consumption device exits.
The control of the energy consumption device body keeps the communication with the flexible direct current protection system at all times, and detects the communication state, when the communication is failed:
the energy consumption device automatically enters autonomous control, the energy consumption device detects the voltage of the direct current bus, when the voltage of the bus is higher than a first threshold value, the control and protection device is put into operation, the voltage is controlled between the first threshold value and a second threshold value, and the second threshold value is larger than the rated value of the voltage of the direct current bus and smaller than the first threshold value. To achieve the control target, the control and protection of the energy consumption device body can adopt pure proportional control or PI control.
When the fault disappears, the receiving end converter station recovers the direct current voltage control capability and can control the direct current voltage to the rated voltage, so that the direct current voltage is reduced below a second threshold value, and the energy consumption device can automatically exit.
The control strategy can automatically adapt to control no matter whether a communication process exists or not, the global sampling advantage of the flexible direct current control protection system is fully exerted when communication exists, energy consumption switching is accurately controlled, direct current voltage is stably controlled, and the energy consumption adaptive control strategy is adopted when communication does not exist, so that direct current voltage control is realized.
A wind power-output direct current transmission system is shown in figure 1 and comprises an offshore wind power plant, a booster station, an offshore flexible direct current converter station 1, a direct current cable, a direct currentenergy consumption device 2, an onshore flexible direct current converter station 3 and an onshore alternating current power grid 4, wherein the direct currentenergy consumption device 2 is installed on one side of the onshore flexible direct current converter station 3.
In this embodiment, a distributed energy consumption device shown in fig. 2 is taken as an example, the energy consumption device may also be a hybrid energy consumption device in which power devices/modules are distributed and energy consumption resistors are concentrated, the direct current energy consumption device in fig. 2 is formed by connecting a plurality ofsub-modules 5 in series, each sub-module is composed of an energy consumption resistor 6, an energy storage capacitor 8 and a controllable device 7, and the energy consumption resistors are switched on to absorb power by controlling the conduction of the controllable devices 7.
Fig. 3 is a schematic diagram of the overall configuration of the energy consumption control system provided by the present invention, the energy consumption control provided by the present invention is composed of a flexible dc control protection system and an energy consumption device control system, when communication is normal, the energy consumption device control system receives a dc energy consumption on-off command and surplus power issued by the flexible dc control protection system, and the energy consumption device control system puts in the number of energy consumption submodules equivalent to the surplus power according to the energy consumption on-off command and the surplus power, thereby controlling dc voltage.
In fig. 3, when the flexible dc control protection system and the energy consumption device control system are in normal communication, the flexible dc control protection system determines whether energy consumption is input and surplus power, so as to avoid the energy consumption device from being input by mistake and accurately calculate the input number, and reduce dc voltage fluctuation. The control method is shown in a flow chart 4, a flexible direct current control protection system firstly monitors whether an alternating current fault occurs or not, the alternating current fault occurs by monitoring alternating current voltage, if the alternating current fault occurs, the flexible direct current control protection system calculates surplus power and direct current voltage, and if the surplus power is larger than a set value and the direct current voltage is larger than an energy consumption input set value, an input instruction is sent to an energy consumption device. And the simultaneous control system sends the calculated surplus power or the number of the sub-modules to the energy consumption device control system.
The voltage control reference value of the direct current bus is U
dc_refSetting the DC rated voltage at U during normal operation
dc_nomThe lower limit of the operation of the voltage of the direct current bus allowed or expected to be controlled by the system is U
dcminUpper limit of U
dcmaxCurrent DC transmission power is P
dcCurrent DC voltage U
dcThe current currently measured for the energy consuming device is I
cp. The nominal number of energy consuming device sub-modules is N. The average voltage of the sub-modules is
When a sub-module is put into operation to consume power, it consumes power
The surplus power calculation formula is as follows:
Prest=Psend-Pdc-Ploss
in the formula, PrestFor surplus power, PsendDelivering power, P, to the current DC system's transmitterdcFor actual power delivery, P, of the receiving converter station during a faultlossIs the loss of the DC cable and the converter station, and can also set PlossWhen the power consumption is set to 0, the loss is considered at the input set value of the power consumption.
When the flexible-direct control protection system monitors that an alternating current fault occurs and detects that surplus is larger than an energy consumption power input set value, Prest≥Pchop_setWhile the DC voltage rises (U)dc≥Udcchop_set1) The flexible-direct control protection system sends an input energy consumption instruction and sends surplus power to the energy consumption device, and the direct current energy consumption device receives PrestAfter the input command is added, the number P of input submodules is calculatedrest/PcmAnd obtaining a basic instruction. On the basis, a command based on the fine adjustment of the difference between the direct-current voltage and the rated voltage is added, and the command can be in a proportional relation or PI control mode to obtain an accurate power command.
And the flexible direct current protection system sends an exit instruction to the energy consumption device after detecting that the fault disappears. And after receiving the quit instruction, the energy consumption device reduces the input sub-module books at a certain speed until the input sub-module books are 0 and quits.
In the above formula, Pchop_setTaking the power of 0 to 0.8 times of soft and direct rated power, Udcchop_set11.02 to 1.5 times of the rated DC voltage is taken. U shapedcmaxTaking 1.05 to 1.5 times of rated direct current voltage, UdcminFrom 0.7 to 0.95 times the rated dc voltage.
When the flexible direct current control system and the energy consumption device control system have communication faults, the control mode is as follows according to fig. 4:
when the communication is interrupted, the energy consumption device can not accept the fault information judgment from the control protection deviceAnd (7) breaking. When a fault occurs, the dc voltage rises. At the moment, the energy consumption device monitors the voltage U of the direct current busdcWhen the DC voltage is higher than Udcchop_set2And after a period of time Tm_set2The energy consuming device is actuated according to Udcchop_set3→Udcchop_set2Corresponding to the corresponding relation of 0 → N submodules, wherein when all the N submodules are put into use, the power consumption of the energy consumption device is equal to the rated transmission power of the direct current system, and the method can realize that the direct current voltage is controlled to be Udc during the fault periodchop_set3To Udcchop_set2In the meantime. When the fault disappears, the power transmission capability of the receiving end direct current voltage control station is recovered, the direct current voltage is reduced, and when the voltage is reduced to Udcchop_set3And after a certain time Tm_set3And the energy consuming device exits.
Udcchop_set2Taking 1.02 to 1.5 times of DC rated voltage, Udcchop_set3Taking 1.01 to 1.3 times of DC rated voltage, Udcchop_set3<Udcchop_set2。Tm_set1Take 0.5ms to 500 ms. T ism_set2Take 0.5ms to 500ms, Tm_set3Take 0.5ms to 500 ms.
The above embodiments are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modifications made on the basis of the technical scheme according to the technical idea of the present invention fall within the protection scope of the present invention.